Effect of Stress Relief on Coal Seam Gas Migration: Experiment and Application Discussion.

Stress relief-induced enhanced permeability is one of the crucial measures for promoting gas desorption flow and strengthening gas extraction. In order to examine the impact of stress relief and its magnitude on gas migration, this article explores the gas desorption flow during the stress relief process and elucidates the influence of stress relief degree on gas extraction. The results indicate that considering the analysis of the pore structure effect on gas seepage, the four coal samples' permeability is ranked as PDS > CSL > JZS > GHS. Throughout the stress relief process, the gas desorption rates of different coal samples under various stress paths exhibit varying degrees of increase. As an illustration, following 3600 s of stress alterations, the gas desorption rate of CSL1# experiences a notable increase, surging by 2.57 times; PDS2# shows 55.93 times increase after 4200 s, and JZS3# exhibits 3.13 times increase after 5400 s. A stress relief degree model is established to investigate the variation of horizontal stress and stress relief degrees under different borehole spacings, vertical stresses, cohesion, and internal friction angles for various borehole diameters (coal output). Optimal stress relief is achieved with a borehole diameter greater than 1.52 m with a borehole spacing set at 4 m. When the stress relief degree exceeds 30%, the corresponding borehole diameter ranges for different vertical stresses are 1.49-1.6 m. Similarly, for cohesion, the ranges are 1.25-1.68 m, and for internal friction angles, the ranges are 1.39-1.53 m. The research results can provide valuable insights for determining parameters in the on-site construction of stress relief boreholes.

Cracking Behavior and Stress Field Evolution in Coal Specimens Containing Bedding under Uniaxial Compression.

During the underground mining process, various coal seams with different bedding structures are often encountered. The presence of bedding structures is one of the primary factors that influence the strength and deformation characteristics of the coal seam and then affect gas extraction and gas disaster prevention. However, there is still a lack of mechanical properties of coal rock with structural anisotropy influenced by bedding structures. In this study, numerical models were established by using the particle flow code method to simulate coal specimens containing bedding with varying inclination angles. The results demonstrate the impact of the bedding inclination angle on the mechanical properties, crack propagation patterns, and the temporal and spatial evolution of the stress field in coal specimens with bedding during the loading process. Furthermore, three crack initiation patterns were investigated for coal specimens with different bedding angles. Additionally, the quantitative relationship between the mechanical properties and the fractal dimension was analyzed. The numerical simulation results were effectively validated through laboratory tests.

Constitutive relation and particle size distribution model of rock fragments in the goaf.

Permeability is considered a key parameter used in goaf flow simulation. Particle size of caved rock fragments is an important factor that affects permeability. Current literature treats the particle sizes of rock fragments as a constant, which is something that will inevitably lead to great errors. The sigmoid function is introduced, based on the existing main roof subsidence displacement model, to establish a new main roof subsidence displacement model, which will reflect the characteristics of the natural accumulation zone, load-affected zone, and compacted zone in the goaf. The constitutive relationship of the rock fragments meanwhile is established from a mechanical perspective. Particle sizes of the rock fragments in the goaf are controlled by the maximum median particle size, with the minimum particle size calculated as 69.25% of the maximum median particle size. In addition, with the same mining height, the stronger the overlying strata is, the larger the particle size, while under the same geological conditions, the larger the mining height, the smaller the particle size of the rock fragments. This paper provides a constitutive relation and particle size distribution model of rock fragments which is more consistent with the actual coal mine's characteristics.

Association of Interleukin-6 Polymorphisms with Schizophrenia and Depression: A Case-Control Study.

OBJECTIVE: Growing evidence suggests a crossover in genetic susceptibility to schizophrenia and depression. We aimed to investigate the association of the rs1800795 and rs1800796 polymorphisms of the IL-6 gene with schizophrenia and depression in the Han Chinese population, combined with IL-6 serum levels. METHODS: Gene sequencing and enzyme-linked immunosorbent assay were performed on 113 subjects with schizophrenia, 114 subjects with depression, and 110 healthy controls. RESULTS: Our findings showed that IL-6 concentrations in schizophrenia and depression groups were significantly higher than in the control group. The rs1800796 CC genotype and C allele were significantly associated with depression (P = .012 and P < .05, respectively). The rs1800796 CC and CG genotype was significantly associated with chronic schizophrenia (P = .020 and P = .009, respectively). Regarding the rs1800795 polymorphism, only one case of CG genotype was detected. The remainder were of the GG genotype. CONCLUSION: The IL-6 rs1800796 might serve as a protective factor for depression and schizophrenia in the Han Chinese population.

Change Laws of Pore-Fracture Structure of Coal under High-Temperature Steam Shock.

Injecting steam into coal seam is an important means to accelerate gas desorption and improve gas extraction efficiency. However, the change law of pore-fracture structures of coal after high-temperature steam shock (thermal shock) is still unclear. Through this study, pore-fracture structures of coal samples before and after thermal shock were compared and analyzed based on the experimental methods of surface pore and fracture extraction, scanning electron microscopy (SEM), and nuclear magnetic resonance (NMR) spectroscopy. The results show that after thermal shock, the surface porosity, max equivalent fracture width, fracture lengths, fracture number, and probability entropy of coal samples increased significantly, and the increment of bituminous coal was greater than that of anthracite. This indicates that thermal shock can promote the development of coal pores, which is significantly better for bituminous coal than anthracite. A SEM analysis reveals that fractures tend to appear at the interface between minerals and coal matrix. The NMR analysis demonstrates that the absolute increment of micropores is the largest, followed by that of mesopores, and that of macropores is the smallest. The increase of porosity in coal shows pore enlargement and penetration, which enhance the connectivity between the pores, thus providing a smoother channel for methane migration. Heterogeneous distribution of mineral components with different thermal expansion coefficients as well as the temperature gradient is the fundamental mechanism behind thermal stress-induced porosity development. The research results provide theoretical support for enhanced gas extraction technology by high-temperature steam injection into coal seams.

Dynamic Evolution of Gas Flow during Coalbed Methane Recovery to Reduce Greenhouse Gas Emission: A Case Study.

Gas pre-extraction technology in a coal reservoir can not only reduce greenhouse gas (GHG) emissions but also effectively recover coalbed methane (CBM). In this work, we use a geomechanical-coupled gas flow (GCF) model to simulate and analyze the pre-extraction effect of a mining-disturbed coal seam. First, the simulation results of the GCF model are compared with field test data to verify the correctness and reliability of our model. Then, the evolution law of the stress field, permeability field, and gas flow field in the extraction process is analyzed through a case study. The results show that the first principal stress of coal in a mining area increases first and then decreases slowly and reaches the peak value at 5 m. The third principal stress increases gradually at first and becomes stable after 10 m. As the distance from the mining face increases, the permeability and gas pressure of the coal seam show continuous and asymmetric "U"-shaped and "n"-shaped distribution characteristics, respectively. In addition, the recovery effect and abnormal emission factors of CBM are discussed. This study can provide theoretical guidance for optimizing the CBM recovery effect and reducing GHG emissions during mining.

Solution for Mass Production of High-Throughput Digital Microfluidic Chip Based on a-Si TFT with In-Pixel Boost Circuit.

As one of the most popular research hotspot of lab-on-chip, digital microfluidic (DMF) technology based on the principle of electrowetting has unique advantages of high-precision, low cost and programmable control. However, due to the limitation of electrodes number, the throughput is hard to further upgrade. Therefore, active matrix electrowetting-on-dielectric (AM-EWOD) technology is a solution to acquire larger scale of driving electrodes. However, the process of manufacturing of AM-EWOD based on thin-film-transistor (TFT) is complex and expensive. Besides, the driving voltage of DMF chip is usually much higher than that of common display products.In this paper, a solution for mass production of AM-EWOD based on amorphous silicon (a-Si) is provided. Samples of 32 × 32 matrix AM-EWOD chips was designed and manufactured. A boost circuit was integrated into the pixel, which can raise the pixel voltage up by about 50%. Customized designed Printed Circuit Board (PCB) was used to supply the timing signals and driving voltage to make the motion of droplets programmable. The process of moving, mixing and generation of droplets was demonstrated.The minimum voltage in need was about 20 V and a velocity of up to 96 mm/s was achieved. Such an DMF device with large-scale matrix and low driving voltage will be very suitable for POCT applications.